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POLARIZED e+/e- SOURCES Jym Clendenin, SLAC

POLARIZED e+/e- SOURCES Jym Clendenin, SLAC. 12 talks related to polarized e- (10) and e+ (2) sources, all but 4 in plenary sessions. 1. Developments for low DF pulsed sources. Higher polarization and QE photocathodes Higher voltage to reduce longitudinal bunching requirements

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POLARIZED e+/e- SOURCES Jym Clendenin, SLAC

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  1. POLARIZED e+/e- SOURCESJym Clendenin, SLAC 12 talks related to polarized e- (10) and e+ (2) sources, all but 4 in plenary sessions

  2. 1. Developments for low DF pulsed sources • Higher polarization and QE photocathodes • Higher voltage to reduce longitudinal bunching requirements • Laser development: ILC requires quasi-cw laser system

  3. 2. Developments for CW sources • Higher average currents • Cathode cooling • Ion back bombardment • Higher voltage

  4. 3. Sources for other applications4. Polarized e+

  5. SL In0.155Al0.2Ga0.645As(5.1nm)/Al0.36Ga0.64As(2.3nm) Yu. Mamaev (SPbSPU)

  6. Increase QE by resonance enhancement of photoabsorption in SL integrated into Fabry-Perot optical cavity.Gerchikov (SPbPU)) Photoabsorption in the working layer: L  1,  - photoabsorbtion coefficient, L - thickness of SL Resonant enhancement by factor 2/(1-(RDBRRGaAs) 1/2)2

  7. Spectra of electron emission, P(), QE()

  8. Resonant enhancement of QE

  9. 1mA from High Polarization Photocathode* * Note: did not actually measure polarization Estimate 48 days with 10 W laser Above 0.5 W need active cooling of cathode Worry about surface charge limit Laser energy Current & vacuum Poelker (JLab)

  10. Limiting Ionized Gas from HV Chamber Beamline Ions Anode Anode = +2kV Support = +300 V Grames (JLab)

  11. Limiting Ionized Gas from HV Chamber Beamline Ions Anode Anode = +2kV Support = +300 V Grames

  12. Lifetime at “EC” at 2mA (~150 C runs) Grames (JLab)

  13. Initial test up to 10 mA, up to 100x more with higher power rf modulator and appropriate laser Kewisch (BNL) • Beam energy 0.8 MeV, current 10 A, limited by availbale RF power • Removable NEA bulk GaAs cathode, 1 mm diameter. • 100 liter cryostat, helium lasts about 24 hours • Beam exits to on top, is bend 90 degrees into a Faraday cup • Focusing with permanent magnet solenoids • NEG pumps inside the cryostat, close to the gun, expected vacuum close to 10-12 torr. • Superconducting ½ cell 1.3 GHz gun

  14. + Enhanced emission Anode e- g + e- - Cathode Material dependence of dark current M. Yamamoto (Nagoya) Dark current = F-N theory Primary field emission Enhanced emission current wisker Ions emission from the anode, secondary electrons and negative ions emission from the cathode. Reduction of primary field emissions Mo Ti Reduction of secondary enhanced emissions

  15. Photocathode Lifetime Preliminary Gun:2.7x10-9Pa 2NEG:2.0x10-9Pa The photocathode lifetime seems no problem under the condition of a few micro amps beam emission. Dark current only ~1 nA @200 kV! M. Yamamoto (Nagoya)

  16. a b 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 22 Time stability of polarization and emission current FE from ultra-thin Fe films on W(100) tip. P=25±5% Total time= 22 hours, max is 3 days and no more days for testing Niu (Hong Kong Univ)

  17. Kuriki (KEK)

  18. 1-m helical undulator Schuler (DESY) Proof of principle experiment (2005) utilizing Final Focus Test Beam at SLAC Compton transmission mode polarimetry for LE photons

  19. Schuler (DESY)

  20. Kuriki (KEK)

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